So, I have had a gold's gym exercise bike for about a year and have used it with great success to lose weight (lost 60 lbs by using it since June), but tonight I came across a problem. When I attempted to use it, it made a weird hissing sound while I was pedaling. When I looked in the part where the pedals were to see what was going on, I found a greenish yellow substance. Would anyone happen to know what is the cause of this? and how to fix it?
The substance wasn't there yesterday and it was not making the hissing sound yesterday, either.

I really hope you didn't squish some bug inside. It would be a good idea to go to the store where you bought it (or any other that has them) and ask them. they should be experienced, especially if they repair them too.